The Low Voltage Ride Through (LVRT) test device of a wind turbine based on power electronics has the advantages of flexible control, high precision, diverse functions and low interference to the power grid. The key problem of the device’s control strategy is how to emulate different kinds of grid-fault voltage waveform as defined in standards. To this end, three-phase and two-phase virtual fault circuits are constructed first. By using the symmetrical component method, the analytical expressions of grid-fault voltage and short circuit impedance ratio of power grid with voltage drop percentage as an input condition are derived in detail. Secondly, the grid fault voltage is taken as the reference value of the voltage drop instruction of the LVRT test device, and the required test voltage waveform can be output through closed-loop control. Considering the LVRT test device of a wind turbine based on modular multilevel converter topology, the control strategy of MMCs connected to the grid and wind turbine separately is provided finally. A simulation model of the LVRT test device for large capacity wind turbines is built, and the effectiveness of the method is verified by simulation of two typical working conditions. This work is supported by the Key Science and Technology Project of China Southern Power Grid Company Limited (No. GDKJXM20193406).